Baling machines which roll fibrous agricultural material into cylindrical bales have been in use for a number of years. One type of roll baler uses a plurality of circulating conveyor belts extending over the whole axial width of the machine, and arranged and driven to define the periphery of a baling chamber into which material is fed from a forward opening in the bottom and in which it is rotated and compressed by the conveyor elements. In another type of baling machine the conveyor elements take the form of cylinders arranged to jointly define by portions of their peripheries a baling chamber for rotating and compressing the material. Machines embodying both of these principals are taught in Sacht U.S. Pat. No. 4,119,026. These machines produce bales which are of light density at the center and increasing outwardly: such bales have a tendency to settle or "squat", thus losing their round outline. The conveyor rollers, being located essentially on a circle about the horizontal axis of the machine, act radially on the material rotating within them to produce a bale having an average density of about ten pounds per cubic foot.